Space electric propulsion plasma characterization using microwave and ion acoustic wave propagation

Electric propulsion is ideal for some space missions due to its high exhaust velocities and efficient use of propellant. Characterization of plasma emissions is important not only for understanding and improving operation of thrusters, but also for understanding how thrusters could potentially impact spacecraft systems. Two diagnostic systems have been implemented to directly characterize high-speed moving plasma plumes. Computer simulations were developed to model experimental results in an attempt at understanding the underlying physics.;The first diagnostic system was used to characterize the plume's influence on a 17 GHz (Ku-band) signal. The phase shift of the microwave signal passing through the plume is measured to find the integrated electron density at spatially resolved points throughout the plume. An Abel inversion algorithm is applied to the integrated phase data to find the local density distribution. Electron density measurements were produced for both an arcjet and space flight qualified stationary plasma thruster (SPT-100). The SPT-100 electron density mapping was fit to a functional form bridging the transition region between the thruster near and far zone transition regions.;The SPT-l00 was investigated to more completely evaluate plume impact on a transmitted signal (a concern for spacecraft communication sub-systems). In addition to the phase measurements, attenuation and power spectral density have been characterized for a number of transmission paths to validate the computer simulations. An electron density model (static and temporal) was applied to a ray tracing analysis which estimates phase shift, attenuation, amplitude, modulation, and phase modulation for a range of frequencies and plume intersection paths.;A second diagnostic system demonstrated the use of ion acoustic wave propagation characteristics to measure flow velocity and electron temperature or ion temperature. The ion acoustic wave is excited and superimposed on the flowing plasma. Phase velocity and flow velocity determine the phase and amplitude pattern of the ion acoustic wave. By characterizing the two quantities, flow velocity and electron or ion temperature can be determined. To estimate an upper bound for ion temperature, the electron temperature is found through implementation of the Langmuir method using the same probe as for the ion acoustic wave excitation.